Incandescent lamp containing iodine, oxygen and inert gas



March 17966 R. P. BONAZOLI ETAL INCANDESCENT LAMP CONTAINING IODINE, OXYGEN AND INERT GAS Filed May 31, 1962 FIG FIG.|

ROBERT P BONAZOLI ROBERT F'. SCOLEDGE JAMES J. PALERMO INVENTORS ATTORNEY United States Patent 7 3,242,372 IN CANDESCENT LAMP CONTAINING IODINE, OXYGEN AND INERT GAS Robert P. Bonazoli, Hamilton, and Robert F. Scoledge, Danvers, Mass., and James J. Palermo, Salem, N.H., assignors to Sylvania Electric Products Inc., a corporation of Delaware Filed May 31, 1962, Ser. No. 198,918 4 Claims. (Cl. 313222) This invention relates to incandescent lamps, particularly to those having an incandescent tungsten filament in an atmosphere of a halogen, or a halogen-containing gas, such as iodine or a gas containing iodine in physical chemical combination, such as an iodide, to keep the envelope from blackening. The amount of iodine needed is quite small, and a gas inert with respect to the filament, such as nitrogen or argon, is generally present also, at a pressure high enough to retard evaporation of the filament. The tungsten evaporated from the filament combines with the iodine to form tungsten iodide before it can deposit on the walls, and the iodide then decomposes at or near the hot filament surface to redeposit on it, thus completing a regenerative cycle.

Such lamps usually have a tubular envelope of quartz or similar material closely placed around a coiled tungsten filament. In such cases, especially when the filament is a concentrated coiled-coil of highpower input per unit length, the tubular envelope becomes overheated and blisters or blows out into a bulbular form at one portion. This appears to be due to a small film of some dark material, probably an impurity in the tungsten, which seems to evaporate from the filament and to deposit on the wall of the glass tube, absorbing some of the radiation and thereby overheating the tube. It may, however, be due to some other cause.

We have discovered that the presence of a small amount of oxygen in the gaseous atmosphere will prevent such overheating and blistering. We find that the amount of oxygen should be between about 0.01% and 1% of the main gas filling for good results. Less oxygen will not achieve the desired result, and more will be deleterious to the filament, causing oxidation or burning, of the tungsten. The most effective amount may vary somewhat with the size of the bulb and the wattage of the filament, and the impurities present in the filament. For example, we have found that an 800-Watt lamp in a T-4 tube about one [and three-eighths inches long operates satisfactorily with about 0.1% oxygen, whereas a 1000-watt lamp in a T-S tube about one and one-half inches long operates better with about 0.4% oxygen. The oxygen percentage is given by weight of the inert gas present; the designations T-4 and T-S have their usual meaning of tubular envelopes foureighths and five-eighths of an inch in outside diameter, respectively.

The length of the tube is taken from one end of the sealed portion to the other, and does not include the flat ends.

The amount of iodine present is quite small, being of the order of one milligram per lamp, as is customary in such devices. The amount of oxygen for best results appears to be independent of the amount of iodine present. We believe that the added oxygen forms oxides with any nickel or other impurities in the tungsten of the filament, thereby putting the impurities in a condition such that they will deposit on the cooler ends of the envelope where they will not interfere with normal lamp operation.

We have also discovered that a slight oxidation of the tungsten filament before sealing the lamp will also give good results. The oxidation should be only suflicient to produce a slight discoloration of the tungsten, and the amount of oxygen present in the oxide should still be ice Within the limits given above when oxygen is .added as a gas.

The increased radiation absorption from the metallic impurities which would otherwise be deposited on the glass can be great enough to decompose tungsten iodide near or at the walls of the lamp tube, thereby defeating the purpose of the iodine in the lamp and still further in creasing the heating.

Other oxidizing agents than oxygen itself can be used provided that the compound formed with the impurities in the tungsten is a stable one, and one that has vapor pressure sufliciently high so that it will deposit at the cool lamp end and not on the middle of the bulb, the portion through which most of the radiation passes. The radiation at angles near the longitudinal axis of the filament coil will be small compared with that emitted laterally from the coil at the middle of the tube.

Although the addition of oxygenhas its greatest effect in lamps of very high wattage input per unit length, or unit area, of the lamp tube, such as in the 800 and 1000 watts lamps, it is also effective in lamps of lower watts input per unit length or area of tube. The main effect in the lamps of lower watts loading may be to reduce blackening during life, but the 650 watt lamps, in T4 bulb about an inch and a half long, will occasionally blister if no oxygen is used. In the 650-watt lamp, the watts loading per square cm. of tube surface is about 60 watts/sq. cm. in the SOO-watt, about 70 watts/sq. cm., and in the 1000-watt about 60 watts/sq. cm. The tungsten at the middle of the 1000-watt lamp tube is about 1200 C.; the corresponding temperature in the 65-watt lamp is about 1000 C., with the temperature at the ends of the sealed part of the tube being about 600 C.

Other objects, advantages and features of the invention will be apparent from the following specification taken in connection with the accompanying drawing, in which:

FIG. 1 shows the blistering which occurs if the oxygen is not used; and FIG. 2 shows a lamp according to the invention.

In FIG. 1, the tubular lamp envelope 1 is seen to have the blister 2 on its envelope, with the discoloration 3. This shows what happens when no oxygen is present in such a lamp of high power input.

In FIG. 2, the tubular lamp envelope 1 has the flattened end portion, 4, 4 through each of which a molybdenum ribbon 4 is sealed as a lead-in conductor. Wires not shown extend from the outside ends of the ribbon 5 to the contact caps 6, 6 which may be of the type described in copending application, Serial No. 192,724 filed May 7, 1962 by Scoledge et al., which also shows the wires from the ribbon 4 to the cup. The flattened ends will generally have the ridges 7, 7 on their outer edge as shown so that the glass when pressed will be roughly parallel with the outside of the tubular envelope 1. This gives the glass pressed out from the flattened portion a place in which to collect and serves also to strengthen the end portions.

The envelope 1 has the customary sealed exhaust tube 9, and is filled with nitrogen at a pressure of say, about one atmosphere, together with a small quantity of iodine. Other pressures and other gases, such as the rare gases, for example, argon, can be used. A 1000-watt lamp whose tubular portion is about five-eighths of an inch in diameter and an inch and a half long, may contain one milligram of iodine, for example. The overall lengths of the glass in the same lamp, including the flattened ends, is about three inches, and the tube wall thickness is about 0.05 inch. The lamp envelope 1 can be of quartz, or of some other suitable material such as a refractory glass consisting almost entirely of silica.

Tungsten wires 8, 8 extend from the inner ends of the ribbons 5, 5 to the inside of the bulb, and the coiledcoil electrically-conducting filament is held between them, one end of the filament fitting over one of the wires 8, the other end over the other wire.

In the T-S lamp previously described for 1000-watt input, the filament 10 is wound of tungsten wire having a diameter of 10.5 mils. This wire is wound at about 60 turns per inch in the usual manner, to have 214 turns in all, to form a primary coil of about 56 mils outer diameter, and then this primary coil is itself wound into a secondary coil of about 0.185 inch outside diameter and is about 0.7 inch long, with 8% turns in that length. Each tungsten wire 8, of about 33 mils diameter, has a curved end that extends into the first 7 or 10 primary turns of the secondary coil as a mandrel would, to make a tight mechanical fit and good electrical connection with the end of the coil 10. The watts loading of the filament coil is about 1300 watts per inch.

The filament is stabilized by being heat-treated in a fixed position as in the copending application Serial No. 674,364, filed July 26, 1957 by W. G. Matheson, now abandoned.

What we claim is:

1. A sealed incandescent lamp containing a halogen vapor, a tungsten filament, a gas inert with respect to the filament and between about 0.01 and 1% of oxygen, the percentage being taken by weight of the inert gas.

2. An incandescent lamp comprising a sealed envelope, and incandescible tungsten filament therein, a gas inert with respect to the filament therein, a small amount of iodine therein, and an amount of oxygen therein between about 0.01% and 1% by weight of the inert gas.

3. An incandescent lamp comprising a sealed tubular envelope, a coiled-coil tungsten filament along the axis of said envelope and close to the wall of said envelope, a gas inert with respect to said filament in said envelope, a small amount of iodine in said envelope, and oxygen in said envelope in an amount between about 0.08% and 1% by weight of the inert gas.

4. An incandescent lamp comprising a sealed tubular envelope, a coiled-coil tungsten filament along the axis of said envelope, at filling of a gas inert with respect to said filament in said envelope, and a small quantity of iodine vapor in said envelope, said envelope also containing a small quantity of a substance which will react with impurities present in the tungsten filament to form a compound therewith which is chemically stable but physically vaporized at the designed operating temperature of the middle portion of the wall of said tubular envelope, the ends of the tubular envelope operating at a temperature sufficiently lower than said middle portion to permit said compound to deposit on said ends and away from said middle portion of said envelope, whereby deposit of said impurities on said wall is prevented.

References Cited by the Examiner UNITED STATES PATENTS 2,170,683 8/1939 Friederich 313223 2,883,571 4/ 1959 Fridrich 313--223 3,132,278 5/1964 Collins et a1 3l3223 X DAVID J. GALVIN, Primary Examiner. 

4. AN INCANDESCENT LAMP COMPRISING A SEALED TUBULAR ENVELOPE, A COILED-COIL TUNGSTEN FILAMENT ALONG THE AXIS OF SAID ENVELOPE, A FILLING OF A GAS INERT WITH RESPECT TO SAID FILAMENT IN SAID ENVELOPE, AND A SMALL QUANTITY OF IODINE VAPOR IN SAID ENVELOPE, SAID ENVELOPE ALSO CONTAINING A SMALL QUANTITY OF A SUBSTANCE WHICH WILL REACT WITH IMPURITIES PRESENT IN THE TUNGSTEN FILAMENT TO FORM A COMPOUND THEREWITH WHICH IS CHEMICALLY STABLE BUT PHYSICALLY VAPORIZED AT THE DESIGNED OPERATING TEMPERATURE OF THE MIDDLE PORTION OF THE WALL OF SAID TUBULAR ENVELOPE, THE ENDS OF THE TUBULAR ENVELOPE OPERATING AT A TEMPERATURE SUFFICIENTLY LOWER THAN SAID MIDDLE PORTION TO PERMIT SAID COMPOUND TO DEPOSIT ON SAID ENDS AND AWAY FROM SAID MIDDLE PORTION OF SAID ENVELOPE, WHEREBY DEPOSIT OF SAID IMPURITIES ON SAID WALL IS PREVENTED. 